noise during acceleration??

[Yaris Revenge]

Every review I've ever read about buzzy engine noises seemed to blame the use of a timing chain. That said, IMHO timing chains are much more desirable than timing belts, despite the noise. Replacing a timing belt (usually recommended ~60k miles) is an expensive to-do, and should you ever have one snap on you, it basically FUBARs your whole engine... pistons and valves get up-close and personal, and all hell breaks loose (literally). Toyota timing chains are so cool, they don't even require maintenance! (or at least that's what they told me about my Vibe/Matrix).

As far as the regular vs. premium, the only difference is how quickly it detonates. Premium burns just a tad slower and more smoothly due to the extra octane molecules tacked on the end of the molecular chain. Regular burns quickly, resulting in more of a "pop" combustion. Maybe that's has something to do with it? If I'm not mistaken, most fuel injected cars have "knock" sensors to detect pre-detonation and electronically adjust the timing to compensate.

~YR